The chroma subcarrier frequency is selected in standard systems including the NTSC and PAL systems such that remanent portions of the chroma carrier within the luminance signal should cancel each other in sequence from line to line or from frame to frame, respectively. This is only effective, however, for transmission of selected scenes. Actually, remanent portions of the chroma signal may remain within the luminance signal so that decoders, particularly such as are used in color television receivers, include a chroma carrier filter or trap in order to draw off such remanent portions, decrease their amplitude, and prevent signals with chroma carrier frequency from reaching the image tube. The resolution of the reproduction is thereby impaired, with respect to the resolution which is available by the overall band widths of the video signal within the respective television system.
It has previously been proposed to separate the chromaticity signal from the luminance signal by means of comb filters. The resolution is retained, yet, other interference phenomena result.
It has also been proposed to conduct the luminance signal of the television signal to a blocking circuit which is damped in dependence on the intensity of the specific color--see, for example, U.S. Pat. No. 3,924,266, Harwood, and corresponding German patent disclosure document DE-OS 25 38 545. Such blocking circuits, however, cause phase errors within the luminance signal so that spurious oscillations may occur when substantial changes in brightness arise in the signal, for example, sudden jumps in luminous intensity.